Process of making iron oxide and sulphur dioxide from iron sulphide ores



Feb.. M, i936. H FREEMAN PROCESS 0F MAKING IRON OXIDE AND SLPHUR DIOXIDEFROM iRoN SULPHIDE oREs Filed MaIOh 5, 1950 search Corporation oiporation lof Canada Application Match s. 1 1o Claim. i

. f This invention relates to improvements in the treatment of sulphideiron ores, such as pyrite and pyrrhotlte and one object oi' the.inventionl is to `eillciently produce simultaneously sulphur 5 dioxideand an iron oxide product, preferably magnetic and" of high iron contentand low sulphur content suitable for production oi' metallic iron.

Various other objects, featuresfa'nd advantages m of the invention maybe ascertained from theA following description.

` This application comprises a 4continuation in part of my fcopendingapplication, led Januaryv -17,- 1929, Ser. No. 333,222, nowv Patent No.1.812,-

,5 397, granted June 30, 1931, the present application embodying certainalternative and additional features and improvemen l In thepast,sulphide iron ores have been largely used in the production 1 of sulphurdioxide by Yroasting or burning the orev withair. Of late,

this has been" accomplishedusually in roosters in which the ore iscaused by mechanical means to move slowly counter current to air. Thistype oi' roaster is welliliustrated in multiple hearth apparatus inwhich `the ore is introduced on the top hearth andmoved Vby rakes acrossthe hearth l to fail onto the hearth below, the operation being.repeated o n each successive hearth. In this and other types otroastersinfgeneral use. the combustion of the sulphide is comparatively slow.

While considerable 'heat is generated, the temv perature oi `theburningsulphide rarely exceeds 1.000 C. and usually does not exceed 700to 800? C. The iron oxide product resulting is in -the' form oi'unfuse'd and unagglomerated small particles varying from` red to purplein colour and is notmagnetic toany appreciable or signiilcant degree'.lIn' the operation oi' .these mechanical roasters, the ore is cold asitenters the roaster;

10 and thus cools the gases leaving the roaster, soV

that acons'iderable partei the sulphur dioxide is oxidized to sulphurtrioxide. At no 'time durjing passage through the rooster ls itordinarily attempted to heat the. ore 'sumcientlv for fusion if, toresult andthe temperature in any part of the urnacels substantially thesame as the tern- V perature of the ore in that part. The solid residualproduct of this treatment is uniused iron oxide containing varyingamountsl oi' sulphur..

o usually'from 2% to 8%.depending' on the ore,

;thetype`ot :toasterl and the mannerot operatiom For example, if itrisdesired to produce from such roosters gasof sulphur dioxide content.

this can be done only by usinga ininimumoi'l higher temperature in the sairand the result isra- MAKING gIlHUB DIOXIDE FROM IRON oi- 'theparticles, relatively widely se pass into contactwith [in the air almostthe -whole volume and are fused. 'I'he oxidized f rima IRON xma AND'mama gan Falls, Quebec, Canols Engineering 'da Re- Canada. Limited, a'corroaster causing somewhat excessive deterlo'ration of the apparatusand a high sulphurresidue in thc iron cxidc product. Y f According tothis invention; the ore, reduced to finely divided form. is burned insuspension` in air during slow passage through a combustion chamber. theamount of alr'being not materially in excess of thatl necessary foroxidation oi all the sulphur and iron. Infthe absence of cooling byexcess of air and by reason of the suspension parated, in hecombusmplete comon is brought'about with liberation of heat air andtheir slow passage through t tion chamber, a very-rapid and co busti Ingreater deta Theore particles" entering the combustion chamber pass rstthrou gh hot gases ilowing to thegas outlet and are thereby heated tothe temperature of ignition and of fusion. The hot particles'then' airand-combustion ensues ai; thesuriaces of the particles. In the finelydivided state in which the ore is treated, the ratio of suiace to'volume isvery high and the particles being relatively widelyseparated-and suspended of each particle, is presented at one time foroxidation, so that Valmost every particle burns completely and all theparticles burn very rapidly. of sulphur is more complete than ispossible with mechanical roasters.- The rapid oxidation liberates heatwhich is absorbed by the particlesand serves to complete and maintain lastate of fusion. 3g In all probability the temperature of the fusedparticlesis higher than can be -obtained by other methods of roasting.This is evidenced lby the factthatthe resulting iron oxide isfound to be,fused, black in colour and highly magnetic. It is 4o known that if rediron oxidei which is non4magc netic, is' heated to or above 1650? C., itis'i'used and converted to a black magnetic oxide and from thislfact itis concluded that, although temperatures of the order of 1650 C. in; thecombustion chamber` may not be recorded, nevertheless the individualparticles have been heated by their heat of combustion to. this orhigher temperature ore particles nally n chamber through are 'therebyVchilled. bc subjected to inaglmination of'non-magnetic mpletely oxidizedparticles silica and other impurities which have en- I6 The removalemerge from the combustio the cool entering air and The produced .oxidemay netic separation tor el material such as ylirico 'and il. theprocess is as follows:-

" cess of air and to the high temperature by rapid and completecombustion of the ore, the` sulphur trioxide that this process is 4formsof apparatus may tered with' the o re. The sulphur content of theproduct is very low, ranging from 0.3% to 12% according to the finenessof the ore. Owing to limitation of the air supply to that necessary inpractice to effect complete combustion of the sulphur and iron, theamount of air admixed with the sulphur dioxide leaving the combustionchamber is much less than in the case of mechanical roasting. Also,owing to the absence of cooling by exattained sulphur dioxide leaves thecombustion chamber at a temperature well above that at which is oxidizesto sulphur trioxide. The exit gases are preferably passed through asteam boiler `wherein the sulphur dioxide is chilled so rapidly throughthe temperature range at which it oxidizes to practically none of thislatter gas is formed. Also. owing to limitation of the air supply, thesulphur dioxide produced by less diluted than that produced frommechanical roasters.

It is found most convenient and practical to =introduce the finelydivided ore vertically downwardly into the top of a combustion chamberby means of a gentle current of air in amount much less than isnecessary for combustion 'of the ore.

' and to supply the further air necessary for combustion by drawing thesame upwardly through the combustion chamber. By adjusting thevelocities of the two opposed air currents relatively to one another andto the force of gravity acting on the particles, the period of timeoccupied by the particles in descending through the combustion chambermay be regulated to provide ample time for combustion. In other words,the de scentof the particles, due to their initial downward velocity andthe acceleration of gravity, may be retarded by the upwardlyv movingcurrent of air.

A form of apparatus which has been found suitable for carrying out theprocess, but to use of which the invention is not confined as other beused,is illustrated more or less .diagrammatically inthe accompanyingdrawing.

Referring more particularly to the drawing, il l designates yo.gas-tight furnace shell. preferably of metal, having a refractory liningi2 and an internal refractory division wall i3 extending from the bottomof the furnace nearly to the top thereof. The dimensions of the furnaceare such that the division wall constitutes two chambers il and i5, the'greatest dimension of each of which is its height. The chamber i4,which is the combustion chamber, ls open .to the atmosphere at thebottom I6 while the chamber I5, which is a settling chamber. is closedto the atmosphere at vits bottom il.. Any suitablemeans for 'coiiectinsand removingthe solid furnace product is provided at suchdistancebeneath lthelcnjainber Ail that it does not interfere with the freeentrance of air into the chamber. Any suitable means I9 is provided atthe-bottom of the chamber I5 for removing solid furnace product whileexcluding air. Conveniently. the means I9 may discharge into the meansIB but this is not obligatory.' A gas cooler 20, preferably in the formof a ilre tube `steam boiler, is connected to the furnace to receivegases from the lower part oi.' the chamber i5. Preferably the boilershell is connected l directly to the furnace shell, as shown. and the alarge exit opening aoaobsv nected to the end of the boiler remote fromthe furnace in such manner as to draw gases from the furnace through theboiler. A damper 22 may be provided between the blower boiler. Theboiler is provided with the usual water supply pipe 23 and steamdelivery pipe 24.

Ore to be treated is delivered in finely divided form into a hopperbottom bin 2 5 from which it is fed through a regulating device 28 intoa hopper 21 open to the atmosphere and connected at its bottom to thesuction inlet of a fan or centrifugal blower 28. The discharge pipe 29of the blower leads downward into the top of the combustion chamber i4and terminates in any suitable sort of heat resisting nozzle 3|).

The operation of the apparatus described is as 2i and the.

follows:-Dry, flnely divided metal sulphide. such as a flotationconcentrate or finely crushed iron pyrites, is delivered to the bin andis fed from the bin at measured rate through 'the regulator 28 into theopen hopper 21, where it is caught by the current of air and drawn intothe blower 2l and fed by it vertically downward into the top of thecombustion chamber Il. By regulating the feeding device 2B andthe speedof the blower 2s, the rate of feed of ore into the furnace and theamount and velocity of air entering with the ore may be regulated asdesired. -The suction of the blower 2i draws air into the bottom of thecombustion chamber and upwardly through this chamber and also drawsv thefurnace gases and any residual air downwardly through the chamber I6 andthrough the boiler 20. The amount and velocity of air entering thebottom of the combustion chamber may be regulatedby means of the damper22 and by regulating the speed of the blower 2i. The regulation ispreferably such that the upwardly movingI current of air offsets theinitial downward velocity of the ore particles feeding finely dividedsulphide downwardly into the combustion chamber with less air thannecessary f'or combustion .of the sulphide and at the same time drawingthe additional air necessary in practice for complete combustion of thesulphide upwardly through the combustion chamber. and the furnace is infull operation, three clearly defined cones-established, the dimensionsof whichI depend on the amounts and velocities of air and sulphidefoci.V

When the temperatures have been built up there are- The upper zone, orheating sone. extends some distance downwardly from the homie 80. Theatmosphere inherent phur dioxide and nitrogen rising` from the zonesbelow. The temperature is too high to permit oxidation ofthe sulphurdioxide by the air enterin g with the sulphide vand little, if any.airrises from vthe zones below. The 'sulphide particles passing downthrough vthis zone are heated to ignition and fusion temperature. Ifthere is free sulphur in the ore. some of it may be volatilized andburned. n

The middle zone. or vzone of primary ombustion, is quite clearly andvisibly defined om the zones above and below.

This zione extends downto this zone is. largely sui- (ifi atf the a.zone of intense combussuipnmdioxide with the sir ustion, extendsdownwerdiy from the level at l Iwhich the sulphide particles becomeincandescent tonearly the bottom ofthe chamber. In this zone the highlyheated particles meet an excess of comparatively undiluted air drawn inat the lbottom of the chamber. 'I'he particles are indi-` viduallyvisible as a shower of brightly sparkling points of light and it ispresumedthat in this zone most of the iron and the residual-sulphur isburned. The intense heat uofthe individual particles, indicated by thecondition 'of incan- .25V desoence, is largely absorbed bythe-particles, at

the moment of liberation, in maintaining the fused state of iron oxideso that the temperature of the atmosphere in this zone is probably muchbelow the temperature of the individual particles.

30 The Ascintillating effect in this zone diminishes toward the bottomof the zone.

Below the bottom zone the fused particles are chilled and solidifiedinthe incoming air and serve in some measure to preheat the air. Thesolid material collected is inthe form of a heavy Vblack powder composedof minute fused particles usually hollow.

'From the foregoing description, it' will be observed that the sulphideis rstburned'with less if air is necessaryfor complete combustion,

the' 'amount being, however, sufficient, for oxidation of moet of thesulphur, andy is later burned tion' of theiron and remainingsulphur. A

It will also beobserved that the sulphide par. '.ticles are maintainedin suspension in air during Ythe entire process ofoxidation. Byregulating 50 the velocities of the two air supplies. the period of timeduring which the particles are held in on, may be `materially longerthan would, be normally occupied in -the gravitation of the particles tothe bottom of the combustion Y with perhaps less air than necessary for'comev plete combustion. the secondary airsupilly being i materially inexcess of that required-foroxida-VA com ar.

runen in wmen most or the with' thev sulphide.andfwitn` the bottom erthe i sores, t here followingmay bepartlcularly noted. The free entranceof air substantially unobstructed by the roasted product at the bottomair inlet Il is such that airmay `be-drawn in over the entire areathrough whiclrthe treated orel falls out of the furnace. `Thus there isfree access of air to all parts of the lower, portionof the furnace andsubstantially uniformly to all areas through which the treated Particlesfall and are chilled during their passage out of the furnace. Yetdespite the fact'thatthis entrance of air `may take place over aconsiderable area. the quantity n of air thus admitted may be carefullyregulated by regulation ofthe damperV 22 Yon the. suction fan 2l, thisregulation being effected without disturbing the uniformity of the draftat one part of the furnace bottom as compared with any other part. Inthetreatment of many forms of it 'isrof advantage to use thesuction-method disclosed, of `drawing the auxiliary air into the bottomof the roasting chamber in lieu of forcing the air into the bottom ofthe chamber. as indicated in my priorpatent above referred That is, bythe suction method, I have found hat the suspension of the ore particlesduring their passage through the `furnace may be made more uniform ateach level in the furnace by using the suction draft at the top ofthefurnace instead of forcing the air in at the bottom of the Vzones oftreatmentabove described are obtained.`

furnace. Also by using the suction fan 2| in lieu of forcing theair inat the bottomof-the furnace, the travel of the gases throughthe settlingchamber I5 and the boiler 20 may be made somewhat more uniform.V Inshort, by properly regulating the damper 22 and by properly adjustingthe-flow of the ore into the apparatus by the regulator 26, the.desirable roasting conditions within the furnace may be readily achievedfor various -grades'of o'resand so that the various With properregulation of the roasting conditions. as above described. therelatively free admission of air-into the bottom ofthe vfurnace also hasthe advantage thatthe ore particles are individuallyl chilled somewhatwhile still in suspension and before the saine reach the.con' Vveyor orother carrying device It. With the individual fused particles thuschilled in suspension, any substantial agglomeration thereof ontheconveyor may be avoided. While theonly oxidizing medium mentioned isair, it willbe obvious that any gas mixture Y which contains'` therequisite free oxygen and no -c. so reduces the time during wmen thestupeur 1 dioxideispassing through the temperature range of oxidationthat practically no sulphur trioxide is formed. l t

0 With the process as carried out in the above described apparatus. thetemperature and time of treatment of the ore in the various zones of theroasting vchamber may be very accurately regulated. There are severalimportant features l to this possibility, among which the `tailwith-respect to particular preferred exampies, l1t winne understood bythose skiuedi in the components which will react undesirably with thesulphide or formed oxides may be substituted `for air. Inthefollowingclaims, the term air"` is to be construed as including such gas Whilethe sulphide introducing current of gas has been stated to be air.it'will be understood that a non-oxidizing gas may be substituted andall 'the oxidizing effect obtained from a countercurrent of oxidizinggas or, alternatively, both of the countercurrents of gas may benonoxidizing and serve merely to maintain the suiphide particlesinsuspension and exposed. to an oxidizingas introduced separately from thetwo countercurrentstreams. l i

While the invention has been described in deart after understanding theinvention. that various changes and further modifications may be l madewithout departing from the spirit and scope of the invention, and it isintended therefore in and modifications.

What is claimed a s new and desired tobe secured by Letters Patent ofthe United States is:

l. A process of oxidizing iron sulphide ores by 'passing the samedownwardly through a roasting chamber of substantial height, whichcomprises introducing the ore in finely divided form into a heated zoneat the top of the chamber where the ore is preheated to ignitiontemperature by contact with rising hot furnace gases, allowing the oreto settle into a second zone in which it is heated to fusion temperatureand burned with a deficiency of gaseous oxidizing agent whereby most ofthe sulphur is oxidized, allowing the ore to settle into athird zone inwhich it is further heated in a state of fusion and is burned with anexcess of gaseous oxidizing agent whereby substantially all of the ironand the remaining sulphur is oxidized, andv finally passing the orethrough an incoming stream` of said' gaseous oxidizing agent as the orepasses out at the bottom of the furnace, said incoming stream being ofsuch temperature that the fused particles are individually chilled whilein suspension suillciently to substantially avoid agglomeration.

2. Process for forming magnetic iron oxide in the form of finely dividedfused particles, which comprises injecting with a gaseous medium finelydivided iron sulphide ore into the top of a hot roasting chamber,allowing said particles to settle in the chamber through a risingcurrent of oxidizing gas, the particles finally passing out at thebottom of the furnace through a relatively cold incoming stream of saidoxidizing'gas. the movement of the ore particles and the gases withinthe chamberbeing so controlled that the sulphur content of the ore islargely burned and the ore particles are individually `fused while insuspension and are then chilled in suspension as they pass out throughthe incoming stream of oxidizing gas. l

3. Process according to claim 2 and in which the gaseous products ofcombustion are withdrawn by suction through an outlet at the ton of thechamber.

a. Process according to claim 2 and in which the gaseous products'ofcombustion are withdawn by suction through an outlet at, the top of thechamber, and including regulating the draft through such outlet toproduce the desired uniform flow of incoming oxidizing gas at the bottomof the chamber.

5. Process of forming magnetic iron oxide in the form of finely dividedfused particles, which comprises roasting finely divided iron sulphideore particles in suspension, the roast being so controlled that theparticles are individually ing the particles to gravitate` against anupwardly flowing stream of relatively `cool oxidiz ing gas of suchtemperature that the -partlcles while still in suspension are chilledsufficiently to avoid agglomeration. i

6. Processof forming magnetic iron oxide in the form of finely dividedparticles, which comprises roasting finely divided sulphide ore parthetemperature of i fused in suspension, and allowi 4 fticles areindividually ticles in suspension in an oxidizing gas, 'at l temperaturecausing fusion of the particles, the particles being allowed togravitate from the area of roasting against an upwardly flowing streamof a relatively cool gaseous medium such that the particles while stillin suspension are chilled sufficiently to substantially avoidagglomeration.

'7. Process of forming magnetic ironl oxide in the form of finelydivided particles but substantially free of dust. which comprisesroasting finely divided iron sulphide ore particles in suspension in anoxidizing gas, at a temperature causing fusion of the particles.allowing the particles to gravitate from the area of roasting against anupwardly flowing. gaseous medium oi' such temperature that the particleswhile still in suspension are chilled sufciently to substantially avoidagglomeration, and withdrawing upwardly by suction means .from the areaof roasting the gaseous products of the roast together with the dustymaterial.

8. Process of oxidizing metal sulphides which comprises introducingthesulphide in finely divided form carried' in a gaseous medium into thetop of a hot combustion chamber, introducing a countercurrent of tosubstantially completely oxidize the sulphides in suspension,withdrawing the gaseous products at the top of the chamber and through asettling chamber by suction means, such a said countercurrent of airbeing maintained by adJusting said suction means so that combustionchamber and the settling chamber is maintained above that at4 whichsulphur trioxide may be formed, and nnally between said settling chamberand suction means passing the gases through means which quickly coolsthem to a temperature below that at which sulphur trioxide forms.

9. Process of oxidizing metal sulphides which comprises vroasting thesame in finely divided form in suspension in an oxidizing gas. at atemperature causing fusion of the particles, allowing the particles togravitate from the area of roastinit4 against an upwardly flowing streamof relatively cool oxidizing gas of such temperature that the particleswhile still in suspension are chilled sufliciently to sugstantiailyavoid agglomeration when collected. withdrawing upwardly from the arealof roasting the gaseous products of combustion together with any dustoccurring at said area. and then passing said products of combustion anddust Adownwardly through a settling chamber.

l0. The process of producing iron oxide in the form of finely dividedfused particles, which comprises oxidizing and roasting finely dividediron sulphide particles in suspension in an atmosphere of oxidizing gas,the temperature of the roasting andloxidfizingbeing sofc'ontrolled thatthe parl fused and Vcaused to be-A come hollow while in Suspension. andthereafter' while the particlesare"still insuspension.` applying. airthereto of such amount that the particles while still in suspen' lsionare chilled sumciently to avoid agglomeraf the temperature in the.

temperature and` stream of relatively cool air in an amount sufficient vssl

